SUMMARY Cardiac fibrosis is a detrimental factor that results in abnormalities in cardiac conduction, stiffening of the ventricular walls, and loss of contractility, thereby contributing to a variety of heart diseases, including hypertrophy, heart failure, and arrhythmia. A variety of stimuli such as infarction, pressure-overload, and oxidative stress can induce fibroblast differentiation and initiate fibrogenesis cascade. A better understanding of the mechanisms of cardiac fibrogenesis will provide novel insight into therapeutic approaches for treatment of fibrosis associated arrhythmia, hypertrophy and heart failure. The goal of this research program is to understand Ca2+ signaling mechanisms in cardiac fibroblasts (CFs) and how Ca2+ signals contribute to cardiac fibrogenesis as well as fibrosis associated heart diseases. In the first funding period, we have made substantial progress in revealing Ca2+ signaling mechanisms in cardiac fibrogenesis. First, we found that TRPM7 is the key Ca2+-permeable channel which is responsible for Ca2+ entry in cardiac fibroblasts. The finding that TRPM7 underlies the molecular mechanism of the major Ca2+- permeable channel in CFs is fundamental because it opens a new avenue for us to explore the potential roles of Ca2+ signals in cardiac fibrogenesis. Second, we found that TRPM7-mediated Ca2+ is required for TGF1 induced fibroblast proliferation, differentiation, and collagen production. Since TGF-1 is the predominant mediator for fibrogenesis, the involvement of TRPM7 in TGF-1 signaling pathway suggests that TRPM7 plays an essential role in cardiac fibrogenesis, and may serve as a therapeutic target. Indeed, we found that TRPM7 mediated Ca2+ signal contributes significantly to fibrogenesis as demonstrated by many lines of evidence, including that TRPM7 is markedly up-regulated in AF patients and that knocking down TRPM7 impairs TGF-1 mediated fibroblasts differentiation and collagen production. These novel findings allow us to ask more profound questions: First, how does Ca2+ signal contribute to fibrogenesis? Second, whether TRPM7 is a potential target for fibrosis related heart diseases. We have designed three specific aims to address these questions in the current application: 1) Investigate if genetically deletion of Trpm7 attenuates fibrosis and improves heart function; 2) Determine the signaling pathways by which TRPM7-mediated Ca2+ signals are involved in cardiac fibrogenesis; 3) Investigate whether TRPM7 influences fibrogenesis by enhancing TGF1 production. We will apply multidisciplinary approaches including molecular biology, biochemistry, patch-clamp, Ca2+ imaging, transgenic and knockout to explore these question at the molecular, cellular, signaling, and in vivo animal model levels. The results of this study will not only reveal how Ca2+ signaling controls cardiac fibrogenesis, but also provide clinical insight into therapeutic approaches for fibrotic heart diseases.